Polycrystalline diamond compacts (“PDCs”), such as cutting elements used in rock bits or other cutting tools, typically include a cemented tungsten carbide substrate having a layer of superabrasive PCD (also commonly referred to as a diamond table) bonded to a surface of the substrate using an ultra-high pressure, ultra-high temperature (“HPHT”) process. Sometimes, the substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing, if desired. A stud carrying a PDC may be used as a subterranean cutting element when mounted to a drill bit by press-fitting, brazing, or otherwise locking the stud into a receptacle formed in the subterranean drill bit or by brazing the cutting element directly into a preformed pocket, socket, or other receptacle formed in the subterranean drill bit. For example, cutter pockets may be formed in the face of a bit formed of cemented tungsten carbide. Generally, a rotary drill bit may include a plurality of PCD superabrasive cutting elements affixed to the drill bit body.
Conventional PDCs are normally fabricated by placing a cemented carbide substrate into a container or cartridge with a volume of diamond crystals or particles positioned on a surface of the substrate. A number of such cartridges may be typically loaded into an ultra-high pressure press. The substrates and volume of diamond particles are then processed under HPHT conditions in the presence of a catalyst material that causes the diamond grains to form and to bond to one another to form a matrix of bonded diamond grains defining a diamond table. The catalyst material is often a solvent catalyst, such as cobalt, nickel, or iron that is used for facilitating the intergrowth of the diamond grains. In one process, a constituent of the substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, becomes liquid and sweeps from the region adjacent to the volume of diamond grains and into interstitial regions between the diamond grains during the HPHT process. The cobalt acts as a catalyst to facilitate the intergrowth process between the diamond grains, which results in bonds between adjacent diamond grains. Often, a solvent catalyst may be mixed with the diamond particles prior to subjecting the diamond particles and the substrate to the HPHT process.
As known in the art, the solvent catalyst may dissolve carbon from the diamond particles or portions of the diamond particles that graphitize due to the high temperatures being used. The solubility of the stable diamond phase in the solvent catalyst is lower than that of the metastable graphite under HPHT conditions. As a result of this solubility difference, the undersaturated graphite tends to dissolve into solvent catalyst and the supersaturated diamond tends to deposit onto existing diamond grains to form diamond-to-diamond bonds. Accordingly, diamond grains become mutually bonded to form a matrix of PCD with interstitial regions between the bonded diamond grains being occupied by the solvent catalyst.
However, the presence of the solvent catalyst in the diamond table can lead to a diamond table that may be thermally damaged at elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the solvent catalyst is believed to lead to chipping or cracking in the PDC during drilling or cutting operations, which consequently can degrade the mechanical properties of the PDC or cause failure. Additionally, it is believed that some of the diamond grains can undergo a chemical breakdown or back-conversion with the solvent catalyst. Of course, at extremely high temperatures, diamond may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof degrading the mechanical properties of the PDC.
Therefore, there is a still a need for a superabrasive material (e.g., PCD) exhibiting superior mechanical and/or thermal properties (e.g., an increased amount of bonding between superabrasive grains).